Stepped frequency radar for landmine detection attached to hexacopter

Danijel Šipoš, Dušan Gleich, Marko Malajner

Univers ity of Mar ibor, S lovenia

16th International Symposium MINE ACTION,Slano, Dubrovnik-Neretva County, 10th April 2019

Outline of presentation• Motivation

• SFCW GPR • Theory

• Design

• Experimental results

• Conclusion• Future work

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Motivation: Idea• Cooperation with Bosnia and Herzegovina (University of Tuzla) where landmines still represent a serious problem

• Why to use RADAR on the drone: • Through the years RF components became even

smaller and more powerful

• Great progress on drones in the last few years

• Use of drones became popular also for many other applications and not only photography

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Possible lift up to 6 kg and flight time up to 20 min

Landmines• Types of landmines• Anti-personnel landmines - CHALLENGE• Anti-tank landmines

• Possible location of landmine• Above ground surface• Below ground surface - CHALLENGE

• Material of landmines• Metal landmines• Plastic landmines – CHALLENGE

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Ground penetrating radar (GPR)• The technical design of ground penetrating radars can be classified into two groups.

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GPR

Time domain

Baseband pulse

Noise-modulated

Frequency domain

SFCW FMCW

Stepped frequency continuous wave (SFCW) GPR

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• Working principle

• SFCW design

• UWB Antenna

• Experimental results

• Problems

SFCW GPR

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• Transmitter output

• Maximal measuring distance

• Resolution

„Synthetic pulse“ of SFCW radar sensor

SFCW GPR: Structures

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• Homodyne SFCW RADAR structure• RF input signal is downconverted once

• Super-Heterodyne SFCW RADAR structure• RF input signal is downconverted twice

• Disadvantages:• IQ imbalance because of phase shifter -> IQ

errors

• Requires a wideband quadrature detector

• Transmiter harmonics can cause ghost effects

SFCW GPR: Design

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• Homodyne structure (SFCW RADAR V1)

• Disadvantages• Ghost effects

• Phase / magnitude noise

SFCW GPR: Design

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• Super-Heterodyne structure (SFCW RADAR V2)• Synthesizer, FPGA, ADC and LO1 use same CLK

fsyn= 700 MHz

fLO1= 702 MHz

fLO2= 2 MHz

fmix_out= 2 MHz

External part

SFCW GPR: Design

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• Hardware parts

• Power

• Processing

• Transmitter

• Receiver

• Specifications

• Power con.: 350 mA

• RF power out.: +2 dBm

• Size: 100x50mm

• fstart = 700 MHz

• BW = 2 GHz

• tstep= 1 - 2 ms

GPR UWB antenna

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• There are many know types of UWB antennas • Resistively loaded dipole antenna• Bow-tie antenna• Spiral antenna• Horn antenna• Log-periodic antenna

Design of GPR antenna

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• Design of combined Horn and Vivaldi antenna

• Design and simulation was carried in CST Microwave Student Edition

A. Ahmed, Y. Zhang, D. Burns, D. Huston, and T. Xia, “Design of uwb antenna for air-coupled impulse ground-penetrating radar,” IEEE Geoscience and Remote Sensing Letters, vol. 13, no. 1, pp. 92–96, Jan 2016.

Antenna 3D model

Design of GPR antenna

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Simulation result

VNA measurement result (700 MHz – 3.9 GHz)

Antenna gain at 2.7 GHz (Max. approximately 9.9 dBi)

SFCW GPR: Solved hardware problems

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• Phase jump after frequency changeSolution: Use of directional coupler and RF switch for measuring a reference signal

• Antenna signal disturbing the receiver part• Solution: Using metal shielding for the SFCW PCB board.

• Antenna coupling• Solution: Antenna shielding between RX and TX antenna

SFCW GPR: Experimental results

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• Test measurement of coaxial cable lenght • Test RADAR measurement of reflector in air

SFCW GPR: Experimental results

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• B-Scan of AT landmine above ground surface• Landmine perimeter: 27 cm

• Landmine height: 13 cm

• Antenna distance to ground surface: 75 cm

AT landmine above ground

Raw Sub. Backg. With Gain

SFCW GPR: Experimental results

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• B-Scan of metal AP landmine above ground surface• Landmine perimeter: 7 cm

• Landmine height: 17 cm

• Antenna distance to ground surface: 75 cm

SFCW GPR: Experimental results

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• B-scan of plastic AP landmine below ground surface• Landmine perimeter: 7 cm

• Landmine height: 5 cm

• Antenna distance to ground surface: 45 cm

AP landmine below ground

Raw Sub. Backg. With Gain

SFCW GPR: Scan problems

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• Antenna distance to ground surface: 75 cm

• B-Scan test of buried metal stick at different antenna height

• Antenna distance to ground surface: 45 cm

Conclusion• The Pulse based GPR as also SFCW based GPR have shown positive results to detect above ground landmines as also buried landmines.

• The goal to develop a small sized GPR with standard IC components (low price) was achieved.

• Challenges• Landmine location

• Antenna to ground distance (Measure at greater distances from the ground surface)

• Future work on hardware improvement as also software improvement

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Conclusion: Future work• Hardware improvements • Metal shielding of whole RADAR system

• Separate shielding of Transmiter, receiver and RF switch

• Software improvements• On board data recording

• Generate random frequency steps ➜ compressive sensing

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Conclusion: Future work

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• Real-time kinematic (RTK) positioning system

• Autonomous flying

• Accurate distance measurement

Thank you!